This invention relates to an improved apparatus for the detection of radon gas in an ambient region using a track registration material.
A known technique employed in the field of radon gas detection which has been found to be highly effective is the method and apparatus for detecting radon and alpha emitting daughters of radon disclosed and claimed in U.S. Pat. No. 3,665,194 to Alter et al. for "Radon Detection", the disclosure of which is hereby incorporated by reference. Briefly, according to this technique a strip of track registration material employed as an alpha particle detector is disposed in a protective environment at a preselected location in order to monitor the presence of radon and alpha emitting daughters of radon. If the track registration material is irradiated by alpha particles falling within a predetermined energy range, minute damage "tracks" are created therein, which tracks can be subsequently enlarged and made visible under suitable magnification by contact with a reagent to which the tracks display preferential chemical reactivity.
Typically, this radon monitoring technique is carried out by placing one or more housings each containing a strip of track registration material in locations to be monitored, such as a mine, and permitting the detectors to remain at the monitored site for a preselected period of time (e.g., several weeks). After exposure, the housings are removed, each strip of track registration material is subjected to a chemical etching solution, and the number of tracks etched on each strip is counted by microscopic inspection. The thus obtained track data is then used to compute the average radon concentration in the monitored site.
While the above described technique has been primarily employed in the past for uranium prospecting applications, recently other applications have been increasingly pursued, albeit primarily on an experimental basis. For example, this technique has been used to measure radon anomalies in earthquake prone areas, to measure radon levels in housing structures located in regions suspected of exhibiting abnormal levels of radon concentration, and as a personal dosimeter to measure the degree of exposure of personnel employed in certain occupations. Recently, increasing interest has been expressed in the monitoring of radon concentration levels within enclosed structures, such as homes, offices and the like, necessitating the preparation of extremely large numbers of track registration type detectors. The most popular, readily available model of such a detector comprises a housing resembling a plastic drinking cup and a strip of track registration material adhered to the inside bottom surface of the cup at a prescribed distance away from the mouth of the cup in order to avoid physical contact with solid particles potentially containing radioactive materials not of interest in a radon survey. These cup detectors, while eminently suitable for ground surveys, are not ideally suited to structural surveys, both from a functional standpoint as well as an aesthetic standpoint. Functionally, the cup must be attached to a wall of the structure or suspended from the ceiling, each of which is at best awkward. The adverse aesthetic effects are deemed obvious. These functional and aesthetic disadvantages are exacerbated by the fact that the detector must be left in place for a prolonged period of time, e.g., three months.